1. Field of the Invention
The present invention relates to a device and method for feeding sheets of paper from a paper tray or cassette. The invention is more particularly related to a paper feeding device and method which changes a pivot point of a base plate supporting a stack of sheets. The invention is also related to a paper feeding device and method in which the position of a separating claw or corner separator is set based on a position of a base plate supporting a stack of sheets.
2. Discussion of the Background
Conventional image forming apparatuses such as printers, facsimile machines, and copiers feed individual sheets from a stack of sheets. However, a problem with conventional feeding mechanisms is that paper jams sometimes occur due to deficiencies inherent to the design of the paper feeding mechanism.
FIG. 1 illustrates a conventional paper tray 1 having a base plate 2 which has thereon a stack of sheets of paper P. The base plate 2 pivots at a pin 5 which passes through a circular hole 4 of a side support 3 connected to the base plate 2. The top sheet from the stack of sheets P is removed by a feed roller 8. A spring 6 is used to raise the base plate 2 in order to keep the stack of sheets P against the feed roller 8.
The base plate 2 has as its pivot point the pin 5. This means that as the base plate 2 is raised from a lowered position as illustrated in FIG. 1, the end of the base plate 2 disposed away from the side support 3 moves closer to the side of the paper tray 1. As the base plate 2 moves upwardly, the lower sheets on the base plate 2 may also contact the side of the paper tray 1. From this raising of the base plate 2, the lower sheets of the stack of sheets P may experience a force illustrated as F in FIG. 1 which moves the sheets away from the side of the paper tray 1. The present inventors have realized that when there are a large number of sheets in the stack P, the weight of the large number of sheets may prevent the lower sheets from sliding due to the force F. If the lower sheets cannot slide, it is possible that the base plate 2 may not be properly raised by the force of the spring 6 and therefore, not properly contact the feed roller 8.
In another conventional paper feeding mechanism as illustrated in FIG. 2, a separating claw 9 is utilized in accordance with the known and conventional corner separation method. In FIG. 2, the separating claw or corner separator 9 can move up and down to a certain extent which is limited by the protrusion 9a which resides between two fixed members 10a and 10b which may be implemented as part of the side of the paper tray 1. In FIG. 2, when the paper tray is completely full, the top of the stack of sheets is at level Y, and when the stack of sheets is nearly exhausted and there remain only a few sheets in the tray, the top sheet will have a position as indicated by Z.
When a sheet is fed when the base plate 2 has a complete stack of sheets thereon, the rotation of the semicircular feed roller 8 about the shaft 8a causes the stack of sheets to be pushed downwardly so that the top sheet of the stack of sheets moves to the position Y', as illustrated in FIG. 3. The separating claw 9 should remain in contact with the top sheet as the stack of sheets is pushed downwardly and therefore, needs to be lowered by a distance designated by a.
When the supply of sheets is nearly used up, as illustrated in FIG. 4, the base plate 2 is angled upwardly toward the corner separator 9. The angling of the base plate 2 results in the lowering of a point of contact of the top sheet and the feed roller 8 when the top sheet is not contacting the feed roller 8. When the feed roller 8 rotates, the top sheet and the base plate 2 are lowered by a distance b which is smaller than the distance a illustrated in FIG. 3. Because the distance or length a is different from the distance or length b, the amount of travel of the separating claw 9 is different. This may result in a different pressure on the sheet between the separating claw 9 and the base plate, depending on the number of sheets in the stack. This difference in pressure along with the different distances the separating claw 9 must travel can make the implementation of the proper pressure of the corner separator difficult, and may cause paper jams.